Macbook and USB Disks

Hi everyone I have a problem. I used my two USB disks this morning to transfer some files to my old 500mHz iBook G3 running 9.2.2. Since then my 2.4gHz Macbook running 10.5.2 wont detect them; they don't show up on the desktop or in disk utility. However my Windows Vista PC, Windows XP virtual machine on my macbook, and the ibook can still detect them. The disks as formatted as FAT32.

How can i get my Macbook to detect my disks again?